Disk-shaped information recording medium, disk cartridge, and information recording/reproducing apparatus

ABSTRACT

The disk-shaped information recording medium having an outer diameter and an inner diameter comprises a substrate having a predetermined thickness, a first side that is one side of the substrate, a second side that is the other side of the substrate, a cylindrical portion forming a through hole formed at a center of the substrate, and a thin portion formed so as to surround an outer diameter of the cylindrical portion. The thin portion is thinner than the predetermined thickness and includes a non-inclined surface and an inclined surface formed on an outer diameter side of the non-inclined surface. The inclined surface is inclined at an angle greater than or equal to 25 degrees and less than or equal to 35 degrees with respect to the non-inclined surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 13/960,814 filed Aug. 7, 2013, which claimspriority under 35 U.S.C.§119 to Japanese Patent Applications No.2012-177029 filed on Aug. 9, 2012 and No. 2013-135367 filed on Jun. 27,2013. The entire disclosures of Japanese Patent Applications No.2012-177029 and No. 2013-135367 are hereby incorporated herein byreference.

BACKGROUND

1. Technical Field

The disclosure relates to a recording medium onto which information isrecorded. Particularly, it relates to a disk-shaped recording medium anda disk cartridge that stores a plurality of disk-shaped recording mediain the stack.

2. Background

An optical disk is constituted by a substrate and a cylindrical portionforming a through hole at a center of the substrate. FIG. 15 shows across section of a known optical disk, as disclosed in Japanese UtilityModel Laid-Open Publication No. H01-103022. A known optical disk has acylindrical portion at its center and an outer side of the cylindricalportion is cut out. Another known optical disk has a label printing areaon one side of the optical disk, as disclosed in Japanese PatentLaid-Open Publication No. H05-198015.

SUMMARY

There is a demand for increasing information storage capacities. As atype of high-capacity information storage, a disk cartridge storing aplurality of optical disks in the stack has been proposed. However,using a plurality of optical disks in a stack, each of which has theabove-described structure, causes adhesion between disks, adherence offoreign particles (e.g. dust), and the like. As a result, the quality ofan optical disk can deteriorate.

The disclosure provides a disk-shaped information recording medium thatassures the quality of the information recording medium, even when theinformation recording medium is placed on another recording medium inuse.

The information recording medium according to one aspect of thedisclosure is a disk-shaped information recording medium having an outerdiameter and an inner diameter. The information recording mediumcomprises a substrate with a predetermined thickness, a first side thatis one side of the substrate, a second side that is the other side ofthe substrate, a cylindrical portion forming a through hole formed at acenter of the substrate, a thin portion formed so as to surround anouter diameter of the cylindrical portion, the thin portion beingthinner than the predetermined thickness, a non-inclined surface formedat the thin portion, and an inclined surface formed on an outer diameterside of the non-inclined surface at the thin portion, the inclinedsurface inclined at an angle greater than or equal to 25 degrees andless than or equal to 35 degrees with respect to the non-inclinedsurface.

The information recording medium according to another aspect of thedisclosure is a disk-shaped information recording medium having an outerdiameter and an inner diameter. The information recording mediumcomprises a substrate with a predetermined thickness, a first side thatis one side of the substrate, a second side that is the other side ofthe substrate, a cylindrical portion forming a through hole formed at acenter of the substrate, a thin portion formed so as to surround anouter diameter of the cylindrical portion, the thin portion beingthinner than the predetermined thickness, a non-inclined surface formedat the thin portion, an inclined surface formed on an outer diameterside of the non-inclined surface at the thin portion, the inclinedsurface being inclined at a predetermined angle to the non-inclinedsurface, a concavo-convex area formed on an outer diameter side of thethin portion on one of the first side and the second side, a printingarea formed in the concavo-convex area, and a data recording area formedon the other of the first side and the second side. The data recordingarea of one of the information recording medium is formed so as not tooverlap the printing area of another one of the information recordingmedium when the one of the information recording medium is placed on theanother one of the information recording medium.

Accordingly, the disk-shaped information recording medium of thisdisclosure is capable of maintaining the quality of the disk-shapedinformation recording medium even when the information recording mediumis placed on another recording medium in use.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of an optical disk according to Embodiment1.

FIG. 2 is a cross sectional view of a central portion of the opticaldisk according to Embodiment 1.

FIG. 3 is a perspective view of a stack of optical disks stored in adisk cartridge according to Embodiment 1.

FIG. 4 is a cross sectional view of the optical disks stacked on top ofanother according to Embodiment 1.

FIG. 5 is a diagram schematically showing a configuration of aninformation recording/reproducing apparatus for an optical disk.

FIGS. 6A to 6F are diagrams for explaining a procedure for separatingoptical disks according to Embodiment 1.

FIG. 7 is a diagram for explaining the state in which foreign particleshave gotten in a thin portion around a central cylindrical portion ofthe optical disk according to Embodiment 1.

FIG. 8 is a cross sectional view of a central part of an optical diskaccording to Embodiment 2.

FIG. 9 is a cross sectional view of a central part of an optical diskaccording to Embodiment 3.

FIGS. 10A and 10B are views schematically showing a clamper in theinformation recording/reproducing apparatus for an optical disk.

FIG. 11 is a view schematically showing a turntable in the informationrecording/reproducing apparatus for an optical disk.

FIGS. 12A and 12B are diagrams for explaining the state in which anoptical disk according to a comparative example is set in theinformation recording/reproducing apparatus.

FIGS. 13A and 13B are diagrams for explaining the state in which theoptical disk according to Embodiment 3 is set in the informationrecording/reproducing apparatus.

FIGS. 14A to 14D are cross sectional views showing central parts ofoptical disks according to other embodiments.

FIG. 15 is a cross sectional view of a known optical disk.

DETAILED DESCRIPTION

Embodiments will be described in detail below with reference to thedrawings as needed. Description that is more detailed than necessary maybe omitted. For example, detailed description of things that are alreadyknown or redundant description of components that are substantially thesame may be omitted. The purpose of this is to avoid making thefollowing description overly repetitive, and to facilitate understandingfor a person skilled in the art. It will be apparent to those skilled inthe art from this disclosure that the following descriptions of theembodiments are provided for illustration only.

Furthermore, the inventors provide the appended drawings and thefollowing description so that a person skilled in the art will fullyunderstand what is disclosed herein, and do not intend thereby to limitthe subject of what is discussed in the patent claims.

Unless otherwise specified, those symbols, labels, and numbers that arethe same in this description indicate the same constituent elements.Also, unless otherwise specified, constituent elements that are notessential to the present invention may not be depicted.

Embodiment 1

Embodiment 1 will now be described below with reference to FIG. 1 toFIG. 7.

1-1. Configuration

1-1-1. Optical Disk

FIG. 1 is a perspective view of the optical disk 10 (an example of adisk-shaped information recording medium) according to Embodiment 1. Theoptical disk 10 is an optical disk such as a Blu-ray Disk (BD), DVD, orCD. The optical disk 10 includes a substrate 11 (an example of asubstrate) having a predetermined thickness and a central cylindricalportion 13 (an example of a cylindrical portion) that forms a throughhole 12. The substrate 11 is formed by injection molding usingtransparent resin such as polycarbonate. The substrate 11 has a firstside (an example of a first side) and a second side (an example of asecond side). The first side of the substrate is formed with a labelprinting area. The second side of the substrate is formed with arecording layer for recording information. The through hole 12 is formedaround a center of the substrate 11. Utilizing the through hole 12, theoptical disk 10 is mounted onto a turntable 150, shown in FIG. 5 andFIG. 11, and described later. As shown in FIG. 2, a thin portion 130 (anexample of a thin portion), that is thinner than the predeterminedthickness of the substrate 11, is formed on an outer diameter side ofthe central cylindrical portion 13 on the first side of the substrate11. The thin portion 130 in this Embodiment is formed on the first sideof the substrate 11, that is, a side having no recording layer forrecording information.

FIG. 2 is a cross sectional view of the substrate 11 illustrating thethin portion 130, formed on an outer diameter side of the centralcylindrical portion 13, according to Embodiment 1. The thin portion 130has a horizontal surface 134 (an example of a non-inclined surface), aninclined surface 132 (an example of an inclined surface) formedcontinuously to the horizontal surface 134, and a vertical surface 133(an example of a vertical surface or a non-inclined surface) formedcontinuously to an inner diameter side of the horizontal surface 134.The horizontal surface 134 has the length “b” from the outer diameter ofthe through hole 12. The horizontal surface 134 extends in parallel to alevel of the side of the substrate 11 where the thin portion 130 is notformed (that is, the second side or the bottom side of the substrate 11shown in FIG. 2). The inclined surface 132 has an angle D so as to beinclined at approximately 30 degrees (preferably between 25 degrees and35 degrees) to the horizontal surface 134. Consequently, the substrate11 is configured to have a cutout on the outer diameter side of thecentral cylindrical portion 13. The vertical surface 133 is formedcontinuously to the horizontal surface 134 and along the outer diameterof the central cylindrical portion 13 that is an outer diameter of thethrough hole 12.

The following is a relation between the length “b” and the length “a”.The length “b” runs from the outer diameter of the central cylindricalportion 13 to an inner edge of the inclined surface 132, which isequivalent to a length of the horizontal surface 134. The length “a”runs from the outer diameter of the central cylindrical portion 13 to anouter edge of the inclined surface 132, which is equivalent to a lengthof the thin portion 130.b<a−b

In other words, the inclined surface 132 is formed larger than thehorizontal surface 134 in the thin portion 130.

Moreover, the length “b” is determined so that the height H1, from thehorizontal surface 134 to a level of the first side of the substrate 11(that is, an upper surface of the substrate 11 shown in FIG. 2), isapproximately equal to the height H2, from a level of the second side ofthe substrate 11 to the horizontal surface 134. The length “b” is 0.4 mmin Embodiment 1. With the configuration, the optical disk 10 is capableof maintaining a certain strength of the substrate 11 while securing aspace formed by the thin portion 130.

In Embodiment 1, the inclined surface 132 is formed so as to be inclinedat about 30 degrees to the horizontal surface 134, the horizontalsurface 134 being parallel to the level of the second side of thesubstrate 11. However, the inclination angle may be any angle between 5degrees and 55 degrees.

1-1-2. Disk Cartridge

FIG. 3 shows a disk cartridge 110 (an example of a disk cartridge)having a case in which a plurality of optical disks 10 are stored in thestack.

The disk cartridge 110 storing the stack of optical disks 10 is set inthe information recording/reproducing apparatus 100 (FIG. 5), which willbe described later.

FIG. 4 shows the state of optical disks 10 stacked one on top ofanother, in which 11 a designates the substrate of an upper optical diskand 11 b designates the substrate of a lower optical disk. The opticaldisk 10, according to Embodiment 1, is used in a disk cartridge 110 thatstores plural optical disks stacked one on top of another. The diskcartridge 110 is used as a high-capacity recording medium of a cartridgetype. In FIG. 4, substrates of only two optical disks (11 a and 11 b) inthe stack are shown for easy understanding. However, the disk cartridge110 may include more than two optical disks.

1-1-3. Information Recording/Reproducing Apparatus

FIG. 5 schematically shows a configuration of the informationrecording/reproducing apparatus 100 (an example of an informationrecording/reproducing apparatus) according to this Embodiment. Theinformation recording/reproducing apparatus 100 includes an opticalpickup drive 101, an optical pickup 102, a motor 104, a turntable 150,and a clamper 160. The information recording/reproducing apparatus 100uses these elements when recording or reproducing information on, orfrom, the optical disk 10. The information recording/reproducingapparatus 100 also includes an electric circuit 103 (an example of anelectric circuit) that controls the recording or reproducing ofinformation on or from the optical disk 10. The informationrecording/reproducing apparatus 100 further includes a separation arm171 and an arm drive circuit 173. The separation arm 171 removes anoptical disk 10 from the disk cartridge 110. The arm drive circuit 173drives the separation arm 171.

The optical pickup 102 is driven by the optical pickup drive 101. Theoptical pickup 102 sends the electric circuit 103 radio-frequencysignals and signals for focusing, tracking, and gap controlling,according to a spatial relationship with the optical disk 10. Inresponse to these signals, the electric circuit 103 sends the opticalpickup 102 signals for driving an actuator for an objective lens. Withthese signals, the optical pickup 102 reads, writes or deletesinformation with respect to the optical disk 10, while performingfocusing control, tracking control, gap control, and tilt control.

As described above, the disk cartridge 110 stores two or more opticaldisks 10 in the stack. Then, the disk cartridge 110 is set in theinformation recording/reproducing apparatus 100 via an operation of auser. The separation arm 171 removes one of the stacked optical disks 10from the disk cartridge 110, under control of the arm drive circuit 173,and carries the removed optical disk 10 to a tray for mounting theoptical disk 10 on the turntable 150. The removed optical disk 10 isthen mounted onto the turntable 150, and ready for being subject toinformation writing or reading by the optical pickup 102.

1-2. Operation

FIG. 6A to FIG. 6F are diagrams for explaining a procedure forseparating the substrates 11 a and 11 b of the stacked optical disksaccording to Embodiment 1. The stacked substrates are separated viaoperation of the above-mentioned separation arm 171. FIG. 6A is a sideview showing the state where the separation arm 171 is inserted in thethrough hole 12 at the center of the stacked substrates 11 a and 11 b.FIG. 6B is a top plan view of the separation arm 171 in the state shownin FIG. 6A. FIG. 6C is a side view showing the state where the stackedsubstrates 11 a, 11 b are about to be separated by the separation arm171. FIG. 6D is a top plan view of the separation arm 171 in the stateshown in FIG. 6C. FIG. 6E is a side view showing the state where thestacked substrates 11 a, 11 b have been separated by the separation arm171. FIG. 6F is a top plan view of the separation arm 171 in the stateshown in FIG. 6E.

As shown in FIG. 6A and FIG. 6B, the separation arm 171 comes down andpasses through the through hole 12 of the upper substrate 11 a, and thenstops at a position just before passing the through hole 12 of the lowersubstrate 11 b.

Then, as shown in FIG. 6C and FIG. 6D, four nails 172 arranged atintervals of about 90 degrees come out from the separation arm 171, andthen extend into an interspace formed by the thin portion 130 forming acutout at a center of the lower substrate 11 b.

Thereafter, as shown in FIG. 6E and FIG. 6F, the separation arm 171 goesup while keeping the extended nails 172 and comes into contact with thebottom side or the second side of the upper substrate 11 a where nocutout is formed. Then, the separation arm 171 goes up together with theupper substrate 11 a held by the nails 172. As a result, the substrate11 a and the substrate 11 b are separated from each other.

As discussed above, it is possible to separate substrates in the stackby utilizing the thin portion 130 formed at the center of the substrate.In order to separate substrates in a proper manner, it is also necessaryto keep a sufficient space at the thin portion 130. However, foreignparticles such as dust accumulated at the thin portion 130 prevent thenails 172 from holding the upper substrate 11 a in a proper position,and this makes the operation of the separation arm 171 unstable, or mayresult in damaging the nails 172.

As described above, according to Embodiment 1, a method of separatingsubstrates 11 of a plurality of stacked optical disks 10 each having athrough hole 12 is provided. The method includes inserting theseparation arm 171 through a through hole 12 of one of the substrates11, pulling out the nails 172 from the separation arm 171 so that thenails 172 extend into a space between the upper substrate 11 a and thelower substrate 11 b, raising the separation arm 171, and thenseparating the stacked optical disks 10 from each other.

The following is a description on how the thin portion 130 of thesubstrate 11 is affected by foreign particles, which will be explainedwith reference to FIG. 7. FIG. 7 shows examples of how the substrate 11according to this Embodiment, and the substrate 61 according to acomparative example, work in the state of being separated and in thestate of being about to be separated. The substrate 11 is a substrateaccording to Embodiment 1, and the substrate 61 is a substrate accordingto a comparative example, the substrate 61 having a horizontal surfaceand a vertical surface with respect to the horizontal surface.

First, the state in which the substrate is separated will be explained.

The state in which the substrate is separated is a state in which thereis only a single substrate. The substrate is in the state of beingseparated, for example, when the optical disk is being moved by theseparation arm 171, or right after the optical disk is moved to a trayfor guiding the optical disk to the turntable 150 (FIG. 4) and is thenmounted on the turntable 150. Alternatively, the substrate may be in thestate of being separated by removing the optical disk from the diskcartridge 110. Additionally, the substrate of the optical disk placed atthe top of the stack is also deemed to be in the state of beingseparated.

In the case of the substrate 11 of the optical disk 10 of thisEmbodiment, foreign particles that have dropped onto the substrate 11will bounce off the inclined surface 132 and move away from thesubstrate 11. Alternatively, the foreign particles may roll down theinclined surface 132 of the substrate 11, then roll on the horizontalsurface 134 that is narrower than the inclined surface 132, and finallyfall off the substrate 11. In other words, the inclined surface 132 ofthe substrate 11 makes it difficult for foreign particles to adhere tothe substrate 11.

On the contrary, as in the case of the substrate 61 of the comparativeexample, foreign particles are likely to remain on the substrate 61after having dropped onto the substrate 61.

Next, the state in which the substrate is about to be separated will beexplained. The state in which the substrate is about to be separated isa state in which, in order to separate the stacked substrates, the nails172 come out of the separation arm 171 and extend into a thin portion ata center of the substrate.

In the case of the substrate 11, of the optical disk 10 of thisEmbodiment, foreign particles on the inclined surface 132 will besubject to the force of the nails 172 in the horizontal direction, sothat the foreign particles will be pushed up along the inclined surface132 by the nails 172.

In the case of the substrate 61 of the comparative example, foreignparticles on the substrate 61 will be moved along the horizontal surfaceby the nails 172 and stuck at the inner side of the horizontal surface.This causes the movement of the nails 172 to stop short, or to deflectin an unintended direction.

As discussed above, the inclined surface 132, of the substrate 11according to this Embodiment, makes foreign particles move easily. As aresult, foreign particles can be prevented from being stuck, and asmooth separation operation can be achieved. Furthermore, because thethin portion 130 includes the inclined surface 132, which is larger thanthe horizontal surface 134, foreign particles can easily fall into thethrough hole at the center to fall off the substrate 11.

As described above, with the inclined surface of the thin portion 130formed at a center of the substrate 11, the optical disk 10 is capableof preventing foreign particles from adhering to and being stuck at thethin portion 130.

The above comparative example differs from Embodiment 1 in theconfiguration of the substrate of the optical disk. A method ofseparating stacked substrates for the comparative example is the same asthe method of separating stacked substrates for Embodiment 1.

1-3. Effects, Etc.

As discussed above, the optical disk 10 according to this Embodimentincludes the thin portion 130 formed on an outer diameter side of thethrough hole 12 at a center of the substrate 11, the thin portion 130has the horizontal surface 134 and the inclined surface 132, and theinclined surface 132 is larger than the horizontal surface 134 in thethin portion 130. Therefore, foreign particles can be prevented fromadhering to, or being stuck at, an inner diameter portion of thesubstrate 11, i.e., around the through hole 12, and the quality of theoptical disk can be prevented from deteriorating.

Moreover, the disk cartridge 110, according to this Embodiment, storestwo or more optical disks 10 in the stack. Each optical disk 10 has thethin portion 130 formed on the outer diameter side of the through hole12 at the center of the substrate 11. Each thin portion 130 has thehorizontal surface 134 and the inclined surface 132. Therefore, even inthe case where the optical disks 10 are used in the stack inside thedisk cartridge 110, the optical disks 10 can be separated in a propermanner. As a result, the optical disks are protected from being damaged,and their quality is maintained.

Embodiment 2

2-1. Configuration

FIG. 8 is a cross sectional view of a substrate 21 (an example of asubstrate) of an optical disk 20 (an example of a disk-shapedinformation recording medium) according to Embodiment 2. The opticaldisk 20 includes the substrate 21, and a central cylindrical portion 23(an example of a cylindrical portion) that forms a through hole 22. Thecentral cylindrical portion 23 is formed with a thin portion 230 (anexample of a thin portion) on the first side of the substrate 21 (anupper side in FIG. 8), similarly to Embodiment 1. The optical disk 10according to Embodiment 2 is different from the previously describedEmbodiment 1, in that the thin portion 230 of the substrate 21 includesthree curvature portions 236, 237, 238 (an example of a curvatureportion). The three curvature portions 236, 237, and 238 are in additionto a horizontal surface 234 (an example of a non-inclined surface) andan inclined surface 232 (an example of an inclined surface) formedcontinuously to the horizontal surface 234. Other parts or elements ofthe optical disk 20 are the same as those of the optical disk 10 ofEmbodiment 1.

The curvature portion 236 is formed between the horizontal surface 234,and a periphery of the through-hole 22, i.e. an outer diameter of thecentral cylindrical portion 23. The curvature portion 237 is formedbetween the horizontal surface 234 and the inclined surface 232. Thecurvature portion 238 is formed between the inclined surface 232 and thehorizontal surface 239 that is a level of the first side of thesubstrate 21, i.e. a side where the thin portion 230 is not formed.

2-2. Effect, Etc.

As discussed above, according to the optical disk 20 of this Embodiment,the thin portion 230 formed at the center of the substrate 21 hascurvature portions 236, 237, 238. With this configuration, in additionto the effects of Embodiment 1, foreign particles can be removed moreeffectively in such cases where the substrate 21 is in the state ofbeing separated or in the state of being about to be separated as shownin FIG. 7. Particularly, with the curvature portion 236, foreignparticles adhering to an inner diameter side of the horizontal surface234 are likely to fall off the horizontal surface 234 and go through thethrough hole 22. With the curvature portion 237, foreign particles canroll down the inclined surface 232 smoothly to the horizontal surface234 without slowing down, then roll on the horizontal surface 234, andfinally come off the substrate 21 by going through the through hole 22.Furthermore, with the curvature portion 238, foreign particles arepushed up obliquely along the inclined surface 232 by the nails 172(FIG. 6) of the separation arm 171 as they are being extended. As aresult, the separation operation by the nails 172, as shown in FIG. 6,is not interfered with by foreign particles remaining on the substrate.

2-3. Modified Example

All of the above described curvature portions 236, 237, and 238 need notbe included. For example, only one or two of the curvature portions 236,237, and 238 may be formed.

Embodiment 3

3-1. Configuration

3-1-1. Optical Disk

FIG. 9 is a cross sectional view of a substrate 31 (an example of asubstrate) of an optical disk 30 (an example of a disk-shapedinformation recording medium) according to Embodiment 3. The opticaldisk 30 has a substrate 31 and a central cylindrical portion 33 (anexample of a cylindrical portion) that forms a through hole 32. Thecentral cylindrical portion 33 forms a thin portion 330 (an example of athin portion) on the first side of the substrate 31 (an upper side inFIG. 9). The thin portion 330 has a horizontal surface 334 (an exampleof a non-inclined surface) and an inclined surface 332 (an example of aninclined surface) formed continuously to the horizontal surface 334. Theoptical disk 30 according to Embodiment 3 is different from the aboveEmbodiments 1 and 2 in that it includes a first protuberance 35 (anexample of a protuberance), a second protuberance 36 (an example of aprotuberance), and a concavo-convex area 51 (an example of aconcavo-convex area).

The first protuberance 35 is formed on an outer diameter side of thethin portion 330 and bulges from the first side of the substrate 31. Thesecond protuberance 36 bulges from the second side of the substrate 31(a lower side in FIG. 9) at a position opposite to the firstprotuberance 35. The second side is further formed with a cover layer 52on an outer diameter side of the second protuberance 36. The cover layer52 includes a data recording area DA (an example of a data recordingarea) where data is recorded or reproduced.

The concavo-convex area 51 is formed on an outer diameter side of thethin portion 330 and the first protuberance 35 on the first side that isa labeling side of the substrate 31 of the optical disk 30. Theconcavo-convex area 51 is formed by a printing method as describedbelow.

The printing is performed according to a common practice using paste.The paste used in this Embodiment contains urethane resin and acrylicresin, the urethane resin 25 to 30% by weight, and the acrylic resin 70to 75% by weight. The paste is applied through the printing method usinga screen printing plate made of polyester, and then the applied paste ishardened by UV irradiation.

The urethane resin used here has a grain size distribution of 3.5micrometers to 5.0 micrometers in average, which forms a concavo-convexshape. When two or more optical disks, with the size of each concaveportion or convex portion being larger than 5 micrometers, are stackedon each other, an information recording side of an upper optical disk ispressed by concave and convex portions formed on an upper side of alower optical disk. As a result, indentation is made on the informationrecording side, which harms the information recorded on the opticaldisk. Moreover, when Si resin is used for the concave and convexportions, some of such concave and convex portions may come off. Forthis reason, urethane resin is used for the concave and convex portionsin this Embodiment.

Moreover, the concavo-convex area 51 is formed within a range of 45millimeters from the center of the substrate 11, for example.

Next, characters are printed on the labeling side that is the first sideof the substrate 31. In this Embodiment, characters are printed throughthe printing method. Characters are printed using the acrylic resinpaste containing pigments. The printed characters are then hardened byUV irradiation. The order of the formation process and the printingprocess for the concavo-convex area 51 may be changed.

The concavo-convex area 51, formed as discussed above, provides aprinting area PA (an example of a printing area) for printing the labelof the optical disk 30 and a clamp area CLA. The label of the opticaldisk 30 is printed in a predetermined radius position. The clamp areaCLA is an area to contact a clamper 160 which will be described later,as shown in FIG. 9. The information printed on the printing area PA isinformation such as a manufacturer's logo, a brand name of the opticaldisk, disk storage capacity, and other similar information related tothe optical disk.

3-1-2. Position of Printing Area

Next is an explanation of a spatial relationship between the printingarea PA on the concavo-convex area 51 on the first side and the datarecording area DA on the second side, in the optical disk 30 accordingto Embodiment 3.

The printing area PA is formed on the above described concavo-convexarea 51 on the first side of the substrate 31. The printing area PA onthe first side of the substrate 31 is formed on an inner diameter sideof the data recording area DA on the second side of the substrate 31such that the printing area PA is at a different radial position fromthe data recording area DA. That is, the printing area PA is formed suchthat an outermost boundary of the printing area PA is located on aninner side of an inner diameter of the data recording area DA.

With the printing area PA and the data recording area DA thus formed,when two or more optical disks 30 are stacked one on top of another, thedata recording area DA on the second side of an upper optical disk 30does not overlap the printing area PA on the first side of a loweroptical disk 30. The printing area PA is formed so that printedcharacters such as a logo protrude from the first side of the substrate31. Therefore, when there is another optical disk placed on thesubstrate 31, a second side of the other upper optical disk adheres tothe printed characters on the substrate 31. This causes a difficulty inseparating optical disks and damages the data recording area DA. Such aproblem can be solved by Embodiment 3 in which when optical disks areused in the stack, the data recording area DA of an upper optical diskdoes not overlap the printing area of a lower optical disk.

3-1-3. Positions of First Protuberance and Second Protuberance

The first protuberance 35 is formed on an inner diameter side of theabove-described concavo-convex area 51 on the first side of thesubstrate 31 of the optical disk 30. When two or more optical disks arestacked one on top of another, the first protuberance 35 prevents thefirst side of the optical disk 30 from sticking to the second side ofanother optical disk placed on the optical disk 30. This makes it easyto separate the stacked optical disks, and prevents a data recordingarea of the other optical disk from being damaged due to sticking.

The second protuberance 36 is formed on an inner diameter side of thecover layer 52 on the second side. When two or more optical disks arestacked one on top of another, and the optical disk 30 is placed onanother optical disk, the second protuberance 36 can prevent the secondside of the optical disk 30 from sticking to the first side of the otheroptical disk. This makes it easy to separate optical disks in the stack,and prevents a data recording area of the optical disk 30 from beingdamaged due to sticking.

Although both the first protuberance 35 and the second protuberance 36are formed on the substrate 31 of the optical disk 30, either one of thefirst protuberance 35 or the second protuberance 36 may singularly beformed.

When both the first protuberance 35 and the second protuberance 36 areformed, one protuberance may be formed with a more sharply-angled topthan the other while the other is formed with an obtuse or flat top.This further makes it easier to separate optical disks in the stack andoptical disks can be stacked on each other in a stable manner. In theexample of FIG. 9, the top of the first protuberance 35 is formed flat,and the second protuberance 36 is formed with a more sharply-angled top.

3-1-4. Position of Clamp Area

Next is an explanation of a spatial relationship between the printingarea PA and the clamp area CLA on the concavo-convex area 51 on thefirst side of the optical disk 30 according to this Embodiment.

The clamp area CLA is formed on the concavo-convex area 51 formed on thefirst side of the substrate 31, as described above, so as not to overlapthe printing area PA. That is, as shown in FIG. 9, the outermostboundary of the clamp area CLA is formed on an inner diameter side ofthe innermost of the printing area PA.

The innermost boundary of the clamp area CLA is formed at the sameposition as the innermost boundary of the concavo-convex area 51, orformed on an outer diameter side of the innermost boundary of theconcavo-convex area 51.

With such positioning of the clamp area CLA as described above, thefollowing effects can be expected.

FIG. 10 schematically shows a configuration of the clamper 160 (FIG. 5)of the information recording/reproducing apparatus 100. FIG. 10A is aplan view of the clamper 160, and FIG. 10B is a cross sectional view ofthe clamper 160. As shown in FIG. 10A and FIG. 10B, the clamper 160includes projections 161 and a metal portion 162.

FIG. 11 schematically shows a configuration of the turntable 150 (FIG.5) of the information recording/reproducing apparatus 100. As shown inthe figure, the turntable 150 includes a central projecting part 151 forholding the central cylindrical portion of an optical disk thereon, anda magnet portion 152 provided on a top of the central projecting part151.

When information is to be recorded on or reproduced from the opticaldisk 30, the optical disk 30 is moved to the top of the turntable 150.From this position, the optical disk 30 is mounted on the turntable 150by insertion of the central projecting part 151 of the turntable 150into the through hole 32 at the center of the optical disk 30. Theclamper 160 descends, and the optical disk 30 is then clamped betweenthe clamper 160 and the turntable 150. At this point, the metal portion162 of the clamper 160 and the magnet portion 152 of the turntable 150attract and adhere to each other, thereby fixing the position of theoptical disk 30. Information is then recorded on or reproduced from theoptical disk 30 while the turntable 150 is rotated by a motor 104.

At this point, the projections 161 of the clamper 160 contact with theclamp area CLA formed on an outer diameter side of the cylindricalportion 33 of the optical disk 30. As previously discussed, the outerdiameter side of the cylindrical portion 33 of the optical disk 30 isformed with the printing area PA.

FIG. 12 shows an example of an optical disk 30′ having a printing areaPA on a clamp area CLA. FIG. 12A shows a plan view of the optical disk30′ in which a printing area PA′ is formed on an outer diameter side ofthe central cylindrical portion 33′. The outer diameter side of thecentral cylindrical portion 33′ forms a central through hole 32′ and theprinting area PA′ is formed in the clamp area CLA. FIG. 12B shows astate in which the optical disk 30′, of FIG. 12A, is on the turntable150 and is clamped by the clamper 160. As shown in FIG. 12, printedcharacters at the printing area PA bulge from the first side of theoptical disk 30′. Therefore, when the projections 161 of the clamper 160come into contact with the bulging printed characters on the opticaldisk 30′, the projections 161 are lifted up by the bulging printedcharacters. This makes the position of the optical disk on the turntable150 unstable.

FIG. 13 shows an example of the optical disk 30 according to Embodiment3. FIG. 13A is a plan view of the optical disk 30 having a clamp areaCLA on an outer diameter side of the central cylindrical portion 33forming a central through hole 32, and a printing area PA on an outerdiameter side of the clamp area CLA such that the clamp area CLA doesnot overlap the printing area PA. FIG. 13B shows a state in which theoptical disk 30 shown in FIG. 13A is on the turntable 150 and clamped bythe clamper 160. As shown in the figure, the clamp area CLA is formed onan inner diameter side of the printing area PA such that the clamp areaCLA does not overlap the printing area PA. As a result, the printingarea PA is prevented from contacting and uplifting the clamper 160, andtherefore, the optical disk 30 on the turntable 150 can be positioned ina stable manner.

The clamp area CLA may be an area of the optical disk 30 which theprojections 161 of the clamper 160 contact. Alternatively, the clamparea CLA may be all the area that not only the projections 161 contactbut also a lower surface 160 a of the clamper 160 having the projections161 face, as shown in FIG. 13B.

3-2. Effects, Etc.

As discussed above, the optical disk 30 according to Embodiment 3 hasthe concavo-convex area 51 formed on an outer diameter side of the thinportion 330 formed centrally on the first side of the substrate 31.Therefore, in addition to the effects of the above-described Embodiments1 and 2, even when the optical disks 30 are used in the stack, theoptical disks 30 can be prevented from sticking to each other and aretherefore easy to be separated.

Furthermore, the optical disk 30 according to Embodiment 3 has a datarecording area DA formed on the second side of the substrate 31 and aprinting area PA formed in the concavo-convex area 51 on the first side.Thus, according to Embodiment 3, the optical disk is formed such thatthe printing area PA is at a different radial position from the datarecording area DA. Therefore, even when plural optical disks 30 arestacked one on top of another, the data recording area DA of an upperoptical disk 30 does not contact the printing area PA of a lower opticaldisk 30. This makes it easy to separate optical disks and prevents thedata recording area DA of the optical disk 30 from being damaged byadhesion to the concavo-convex area 51.

Furthermore, the optical disk 30 according to Embodiment 3 has the clamparea CLA formed on the first side of the substrate 31 so as not tooverlap the printing area PA. Therefore, the optical disk 30 can be setin the information recording/reproducing apparatus 100 in a stablemanner.

3-3. Modified Example

The clamp area CLA may be formed on an outer diameter side of theprinting area PA so as not to overlap the printing area PA, according toa configuration of the clamper.

Other Embodiments

(1)

In the optical disk according to the above Embodiments, the thin portionformed at a center of the substrate has a horizontal surface and aninclined surface, the inclined surface larger than the horizontalsurface. Alternatively, the thin portion may be formed with a horizontalsurface and an inclined surface that is equal in size to or smaller thanthe horizontal surface.

(2)

A configuration of the thin portion formed at the center of thesubstrate of the optical disk should not be limited to the configurationin the above-described Embodiments. For example, the thin portion asfollows will have the same effects as the above-described Embodiments.

As cross-sectionally shown in FIG. 14A, the thin portion 430 formed atthe center of the substrate 441 is formed with an inclined surface 432(an example of an inclined surface) inclined at a predetermined angle,and a vertical surface 433 (an example of a non-inclined surface) formedcontinuously to an inner diameter of the inclined surface 432 and alongan outer diameter of the central cylindrical portion 443, i.e. an outerdiameter of the through hole 442.

As cross-sectionally shown in FIG. 14B, the thin portion 530 formed atthe center of the substrate 551 is formed with inclined surfaces 532 a,532 b (examples of inclined surfaces) inclined at different angles, anda vertical surface 533 (an example of a non-inclined surface) formedcontinuously to an inner diameter of the inclined surface 532 a andalong an outer diameter of the central cylindrical portion 553, i.e. anouter diameter of the through hole 552.

In FIG. 14B, the thin portion 530 may also be described as including aninclined surface 532 a (an example of a third surface) and an inclinedsurface 532 b (an example of a fourth surface), in which the inclinedsurface 532 a and the inclined surface 532 b are inclined at differentangles.

Alternatively, as cross-sectionally shown in FIG. 14C, the thin portion630 formed at the center of the substrate 661 is formed with an inclinedsurface 632 (an example of an inclined surface) inclined at apredetermined angle, a vertical surface 633 (an example of anon-inclined surface) formed continuously to an inner diameter of theinclined surface 632 and along an outer diameter of the centralcylindrical portion 663, i.e. an outer diameter of the through hole 662,and a vertical surface 635 (an example of a non-inclined surface) formedcontinuously to an outer diameter of the inclined surface 632 andextending vertically from the inclined surface 632 to a level of thefirst side of the substrate 661.

(3)

In the above-described Embodiment, the thin portion of the substrate ofthe optical disk is formed by reducing the thickness at a center of thefirst side of the substrate. Alternatively, the thin portion may beformed on the second side of the substrate, with which the optical diskwill have the same effects. Furthermore, a two-sided optical disk ascross-sectionally shown in FIG. 14D will have the same effects as thoseof the above-described Embodiments. Particularly, the two-sided opticaldisk has a thin portion 730 formed on both sides of the center of thesubstrate 730. The thin portion 730 includes inclined surfaces 732 a,732 b and non-inclined surfaces 734 a, 734 b at the both sides of thethin portion respectively, and a through hole 762 formed by a verticalsurface 733 that is an inner diameter of the thin portion 730 and formedat a center in the thickness direction of the substrate 761.

(4)

In the above-described Embodiment, an optical disk is given as anexample of the disk-shaped information recording medium. However theexample should not be limited to an optical disk. As far as it is adisk-shaped information recording medium, any medium such as a magneticdisk or a magnetic optical disk may be applied.

(5)

The above-described Embodiments are given as examples of the techniquedisclosed herein. The accompanying drawings and detailed descriptionthereof are provided only for describing the Embodiments. Accordingly,the constituent elements shown in the accompanying drawings anddescribed in the detailed description may include not only thosenecessary for solving the technical problems but also those that are notessential for solving the technical problems and only given forillustrating the technique. Therefore, the constituent elements shouldnot be considered as essential elements only because they are shown inthe drawings and described in the detailed description.

The foregoing descriptions of the Embodiments are provided forillustration only, and therefore, various changes, substitution,addition, omission or the like can be made herein without departing fromthe scope as defined by the appended claims and their equivalents.

The disclosed technique may be applied to a disk-shaped informationrecording medium and an information recording/reproducing apparatus forthe disk-shaped information recording medium.

GENERAL INTERPRETATION OF TERMS

In understanding the scope of the present disclosure, the term“comprising” and its derivatives, as used herein, are intended to beopen ended terms that specify the presence of the stated features,elements, components, groups, integers, and/or steps, but do not excludethe presence of other unstated features, elements, components, groups,integers and/or steps. The foregoing also applies to words havingsimilar meanings such as the terms, “including”, “having” and theirderivatives. Also, the terms “part,” “section,” “portion,” “member” or“element” when used in the singular can have the dual meaning of asingle part or a plurality of parts. Also as used herein to describe theabove embodiment(s), the following directional terms “forward”,“rearward”, “above”, “downward”, “vertical”, “horizontal”, “below” and“transverse” as well as any other similar directional terms refer tothose directions of the disk-shaped information recording medium, diskcartridge, and information recording/reproducing apparatus. Accordingly,these terms, as utilized to describe the technology disclosed hereinshould be interpreted relative to the disk-shaped information recordingmedium, disk cartridge, and information recording/reproducing apparatus.

The term “configured” as used herein to describe a component, section,or part of a device includes hardware and/or software that isconstructed and/or programmed to carry out the desired function.

The terms of degree such as “substantially”, “about” and “approximately”as used herein mean a reasonable amount of deviation of the modifiedterm such that the end result is not significantly changed.

While only selected embodiments have been chosen to illustrate thepresent invention, it will be apparent to those skilled in the art fromthis disclosure that various changes and modifications can be madeherein without departing from the scope of the invention as defined inthe appended claims. For example, the size, shape, location ororientation of the various components can be changed as needed and/ordesired. Components that are shown directly connected or contacting eachother can have intermediate structures disposed between them. Thefunctions of one element can be performed by two, and vice versa. Thestructures and functions of one embodiment can be adopted in anotherembodiment. It is not necessary for all advantages to be present in aparticular embodiment at the same time. Every feature which is uniquefrom the prior art, alone or in combination with other features, alsoshould be considered a separate description of further inventions by theapplicants, including the structural and/or functional concepts embodiedby such feature(s). Thus, the foregoing descriptions of the embodimentsaccording to the present invention are provided for illustration only,and not for the purpose of limiting the invention as defined by theappended claims and their equivalents.

What is claimed:
 1. A disk-shaped information recording medium having anouter diameter and an inner diameter, the information recording mediumcomprising: a substrate having a predetermined thickness; a first sidethat is one side of the substrate; a second side that is the other sideof the substrate; a cylindrical portion forming a through hole formed ata center of the substrate; a thin portion formed so as to surround anouter diameter of the cylindrical portion, the thin portion beingthinner than the predetermined thickness; a non-inclined surface formedat the thin portion; and an inclined surface formed on an outer diameterside of the non-inclined surface at the thin portion, the inclinedsurface inclined at an angle greater than or equal to 25 degrees andless than or equal to 35 degrees with respect to the non-inclinedsurface.
 2. The disk-shaped information recording medium according toclaim 1, further comprising a curvature portion formed between thenon-inclined surface and the inclined surface.
 3. The disk-shapedinformation recording medium according to claim 1, further comprising acurvature portion formed between the inclined surface and a surface ofthe substrate where the thin portion is not formed.
 4. The disk-shapedinformation recording medium according to claim 1, further comprising aprotuberance formed on an outer diameter side of the thin portion on atleast one of the first side and the second side, the protuberancebulging from the at least one of the first side and the second side. 5.The disk-shaped information recording medium according to claim 1,further comprising a concavo-convex area formed on an outer diameterside of the thin portion on either one of the first side or the secondside.
 6. The disk-shaped information recording medium according to claim5, further comprising: a data recording area formed on the other one ofthe first side or the second side; and a printing area formed in theconcavo-convex area such that the printing area is at a different radialposition from the data recording area in the information recordingmedium.
 7. The disk-shaped information recording medium according toclaim 5, wherein a diameter of each convex portion or each concaveportion in the concavo-convex area is within 3.5 micrometers to 5.0micrometers.
 8. The disk-shaped information recording medium accordingto claim 5, wherein the concavo-convex area contains urethane resin. 9.The disk-shaped information recording medium according to claim 5,wherein the concavo-convex area is formed within a range of 45millimeters from the center of the substrate.
 10. The disk-shapedinformation recording medium according to claim 1, further comprising: aconcavo-convex area formed on an outer diameter side of the thin portionon either one of the first side or the second side; a printing areaformed in the concavo-convex area; and an area formed on an innerdiameter side or an outer diameter side of the printing area in theconcavo-convex area, the area being contacted by a clamper wheninformation is recorded on or reproduced from the information recordingmedium.
 11. A disk cartridge-comprising: a plurality of the disk-shapedinformation recording media according to claim 1; and a case that storesthe plurality of the disk-shaped information recording media stacked oneon top of another.
 12. An information recording/reproducing apparatus,comprising: the disk cartridge according to claim 11; a mechanismconfigured to remove one of the disk-shaped information recording mediafrom the disk cartridge; a mechanism configured to record or reproduceinformation on or from the removed one of the disk-shaped informationrecording media; an electric circuit configured to control the recordingor reproducing of information on or from the removed one of thedisk-shaped information recording media.